1. Field of the Invention
The present invention relates to an imaging apparatus with a shake compensation function for detecting and compensating for shake of the imaging apparatus.
2. Description of the Related Art
Among conventional imaging apparatuses with shake compensation, there are cameras, for example.
An anti-shake function for suppressing image blur on an imaging plane is known as a shake compensation function implemented in a camera. The anti-shake function uses angular velocity sensors or the like to detect camera shake in pitch and yaw directions, respectively. Then, based on their output signals, part of an image taking optical system or an image pickup element is shifted independently in directions to cancel out the horizontal and vertical camera movements on a plane perpendicular to an optical axis, thereby compensating for camera shake.
The angular velocity sensor used in a video or still camera for detecting camera shake is small and cheap, but it could superpose a drift component on the output signal. The drift component is a change of the voltage when the angular velocity is null (that is, a change of the output signal when the camera is at rest) mainly caused by a change in ambient temperature. In this case, it is necessary to remove the drift component because it results in an error in camera shake detection.
For example, one of methods for removing the drift component is disclosed in Japanese Patent Laid-Open No. 10-90743. In this method, as shown in FIG. 12, the moving average value of an output signal from an angular velocity sensor 101 is calculated to determine a reference value at which the angular velocity goes to zero, and the reference value is subtracted from the output signal from the angular velocity sensor 101 to remove the drift component. Then, using the subtracted value, an integral operation is performed to convert the angular velocity signal to an angular displacement signal so as to calculate the amount of compensation while taking into account camera information such as the focal length of an imaging lens. Then, from target driving position information on an anti-shake lens obtained as the calculation result, position information on the anti-shake lens detected by a position detector 102 is subtracted, and the subtracted value is output to a compensation driving unit 103 to compensate for camera shake.
The camera-shake compensation includes motion picture compensation applied to the compensation during framing operation for moving picture capturing or still picture capturing, and still image compensation applied to the compensation during an exposure process. Both are required to achieve different levels of compensation performance. The still image compensation is required to fully compensate for image blur caused during the exposure, while motion picture compensation is required to keep an acceptable level of compensation performance for a long period of time, but not necessarily required to achieve the perfect compensation.
Therefore, in order to compensate for motion picture blur, it is preferable to mainly compensate for high-frequency fluctuating components of relatively small amplitude. In other words, in case of motion picture compensation, if the reference value is drastically changed in response to a big fluctuation in the output signal from the angular velocity sensor as shown in FIG. 4A, it is enough to compensate only for high-frequency components of the fluctuating signal from which the reference value has been subtracted as shown in FIG. 4B.
On the other hand, in case of still image compensation, an image without the effects of camera shake causing image blur cannot be obtained unless the reference value agrees with an angular velocity value of zero.